Compressors to compress working fluid such as a refrigerant are used in various apparatuses. Refrigeration cycle apparatuses such as refrigerating machines, water heaters, and air conditioners employ scroll compressors as a device to compress refrigerant gas.
A scroll compressor includes: a fixed scroll including a spiral wrap stood on an end plate (a base plate); and an orbiting scroll including a spiral wrap stood on an end plate (a sliding plate). The scroll compressor has a structure in which the fixed scroll and the orbiting scroll are arranged to face each other so that the wraps thereof engage with each other. In the scroll compressor, the orbiting scroll orbits to sequentially reduce the volumes of a plurality of compression chambers formed between the wraps, thereby compressing the refrigerant.
Such compression operation produces axial force (hereinafter, referred to as “separating force”) which attempts to separate the fixed scroll and the orbiting scroll from each other. In addition to the axial force (separating force), tangential force, radial force, and centrifugal force are applied to the orbiting scroll by the compression operation. These forces produce a moment (an upsetting moment) that attempts to tilt the orbiting scroll. The orbiting scroll thereby swings. If the scrolls are separated from each other, a gap is formed between the end (the end surface) of the wrap and the bottom thereof. Accordingly, the sealing performance of the compression chambers cannot be maintained, and the refrigerant leaks in the compression chambers (especially in the vicinity of the suction chamber where the seal length is short). The efficiency of the compressor is thereby reduced.
In view of this, a backpressure chamber is formed, on the back of the sliding plate of the orbiting scroll, to hold backpressure to press the orbiting scroll against the fixed scroll. The backpressure is pressure within the backpressure chamber and takes an intermediate value between the discharge pressure and the suction pressure. In the scroll compressor having this structure, the orbiting scroll is pressed against the fixed scroll with the backpressure within the backpressure chamber to cancel out the separating force and produce a force (hereinafter, referred to as pressing force) to press a sliding surface of the orbiting scroll against a sliding surface of the fixed scroll. In the scroll compressor having this structure, the refrigerant leakage loss can be reduced in the compression chambers (especially in the vicinity of the suction chamber where the seal length is short) by the pressing force. Herein, the sliding surface of the fixed scroll is a surface formed so as to continue to the end surface of the wrap of the fixed scroll. The sliding surface of the orbiting scroll is a surface of the outer peripheral portion of the sliding plate of the orbiting scroll which comes into contact with the fixed scroll.
However, the pressing force produces sliding friction between the sliding surface of the fixed scroll and the sliding surface of the orbiting scroll. When the pressing force excessively increases, the sliding loss increases, and the performance of the compressor decreases.
Accordingly, a scroll compressor is proposed which includes a backpressure introduced space on the sliding surface of the fixed scroll or the orbiting scroll. To the backpressure introduced space, the pressure (backpressure) within the backpressure chamber is introduced. This increases the pressing force in a region where a lot of refrigerant leaks between the sliding surfaces to reduce the refrigerant leakage loss in the compression chambers (Patent Document 1, for example). In the scroll compressor having this structure, the refrigerant leakage loss in the compression chamber (especially in the vicinity of the suction chamber where the seal length is short) and the sliding loss can be reduced.